As a conventional magnetic core material for the reactor, a stacked electromagnetic steel plate or a soft magnetic metal power core can be used. Although the stacked electromagnetic steel plate has a high saturation magnetic flux density, the iron loss becomes greater if the driving frequency of the power supply circuit exceeds 10 kHz, causing the decrease of efficiency. The soft magnetic metal powder core is widely used with the driving frequency being higher because its iron loss at a high frequency is less than the stacked electromagnetic steel plate. However, the iron loss may not be low enough, and some problems are there such as its saturation magnetic flux density is inferior to that of the electromagnetic steel plate.
On the other hand, the ferrite core is well known as a material for magnetic core with a small iron loss at a high frequency. However, the ferrite core has a lower saturation magnetic flux density compared to the stacked electromagnetic steel plate or the soft magnetic metal powder core, so a design is needed to provide a relatively large sectional area of the core so as to avoid the magnetic saturation when a large current is applied. In this respect, a problem arises that the shape becomes larger.
In Patent Document 1, a reactor has been disclosed which uses a composite magnetic core as the material for the magnetic core so that the loss, size and the weight of the magnetic core are reduced, wherein the composite magnetic core is obtained by combining a soft magnetic metal powder core which is used for the coil winding portion and a ferrite core which is used for the yoke portion.